Accumulators



April 30, 1957 B. N. ASHTON 2,790,462

ACCUMULATORS Filed Feb. 18, 1953 2 Sheets-Sheet l FIG. I.

- INVENTOR. BENJAMIN N. ASHTON April 30, 1957 B. N.ASHTON 2,790,462

ACCUMULATORS Filed Feb. 18, less 2 Sheets-Sheet 2 FIG. 3.

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nu 1 k N INVENTOR. T BENJAMIN N. ASHTON ATTOZNEYS QMJ MVQW United States Patent ACCUMULATORS Benjamin N. Ashton, Kingston, N. Y., assignor to Electrol Incorporated, Kingston, N. Y., a corporation of Delaware Application February 18, 1953, Serial No. 337,553

3 Claims. (Cl. 138-31) This invention relates to improvements in accumulators for hydraulic systems and it relates particularly to piston-type accumulators suitable for use in high and low pressure hydraulic systems.

Piston-type accumulators are well known in the industry but they have certain disadvantages which have prevented their widespread use. The prior piston-type accumulators must have accurately ground or honed cylinders and pistons and precisely fitted piston rings to prevent leakage of the hydraulic liquid and the gas in the accumulator past the rings of the piston. Such structures are prohibitively expensive, and even when made with the greatest of care they are not entirely effective in preventing mixing of the gas and the liquid in the accumulator.

In my Patent No. 2,440,065, dated April 20, 1948, I disclose a piston type of accumulator which overcomes, to a large degree, the difiiculties previously encountered in providing leak-proof piston and piston ring assemblies. The accumulator disclosed in my patent is highly effective in preventing leakage of the gas and the liquid past the piston rings under conditions of high pressure operation, such as for example, in the high pressure hydraulic systems used in aircraft. However, even my prior accumulator is not entirely free from leakage and mixing of the gas and liquid when the pressure differential between the atmosphere and the pressures of liquid and gas on opposite sides of the piston rings is small. Moreover, from a practical standpoint, the cylinder and cylinder head assemblies disclosed in the patent present some dangers when servicing of the accumulator is required. Thus, for example, it has been found that maintenance men will unscrew the cylinder heads while pressure still remains in the accumulator. As a result, the cylinder head may be blown loose by the pressure in the accumulator and the maintenance man may be in-' jured by the cylinder head or piston.

The present invention relates to improved accumu-' lators in which an effective seal may be obtained even when the accumulator is used in a low pressure hydraulic system. Moreover, the new accumulators are provided with cylinder heads which cannot be removed until the pressure in the accumulator is reduced to a safe value. In addition, I have provided an improved accumulator in which the need for honing the entire interior surface of the cylinder, or an extended surface area of the piston is reduced to a minimum so that the accumulator can be produced at greatly reduced cost and much more quickly than heretofore.

For a better understanding of the present invention, reference may be had to accompanying drawing, in which:

Fig. l is a view in longitudinal section of a typical accumulator embodying the present invention;

Fig. 2 is a view in end elevation of the accumulator illustrating the means for retaining the cylinder head in the accumulator cylinder;

Fig. 3 is a view in section through a modified form of accumulator embodying the present invention; and

2,790,462 Patented Apr. 30, 1957 Fig. 4 is a view in longitudinal section of still a further form of accumulator.

opposite ends to receive therein the cylinder heads 11 and 12. Mounted in the interior of the cylinder 10 for sliding movement lengthwise thereof is a piston 13 having a closed head 14 and a hollow cylindrical skirt 15. If desired, both ends of the piston may be closed. The cylinder 10 is provided with an inwardly extending annular land or bearing surface 16 at its mid-portion which is in sliding engagement with the skirt 15 of the piston 13. The piston 13 is of sufiicient overall length that its skirt is in contact with the land or bearing surface 16 in any position of .the pistonlengthwise of the cylinder. The piston is otherwise spaced from the wall of the cylinder by a small amount, on the order of a few thousandths of an inch. Inasmuch as the piston 13 is in sliding contact with the land or bearing surface 16, and is out of sliding contact with the remainder of the cylinder wall, only the skirt of the piston and the surface of the land 16 need to be ground and honed to close tolerances. The remainder of the cylinder can be left unfinished or in a roughly machined condition. Inasmuch as it is much easier to hone a'small surface within close limits or tolerances, a cylinder of the type disclosed in Fig. 1 can be produced easier and at much lower cost than a cylinder in which the entire inner surface must be honed or otherwise finished to obtain a precise fit with the piston.

In order to effect a tight seal with the piston, the surface of the land or bearing surface 16 is provided with a pair of parallel grooves 17 and 18, to receive O-ring seals 19 and 20 formed of rubber, synthetic rubber, or the like. While the O-ring type of seal is preferred, other similar compressible sealing means, such as chevron type seals, U-type seals, or similar seals formed of compressible or resilient material, may be used with equal success. All such seals will be referred to hereinafter as compressible seals or compressible sealing rings. The compressible seals 19 and 20 are received loosely in the grooves 17 and 18 and bear against the skirt 15 of the piston. The grooves 17 and 18 are wider than their depth so that the rings are slightly compressed between the surface of the skirt of the piston 15 and the bottoms of the grooves, but can move transversely of the grooves 17 and 18. Such seals alone are not completely effective in preventing leakage of gas or liquid past them. Accordingly, as explained in my Patent No. 2,440,065, a passage 21 is formed through the wall of the cylinder between the compressible seals 19 and 20. In this way, the space between the seals 19 and 20 is maintained at atmospheric pressure and the seals are compressed tightly against the the skirt of the piston and the bottom and the inner walls of the grooves 17 and 18 by the pressure of gas on one side of the piston and liquid on the other side of the piston, thereby reducing leakage past the seals to a minimum. While from a production standpoint, it is preferable to mount the compressible seals 19 and 20 in the raised land 16, as explained above, it is also possible to mount them in grooves adjacent the mid-portion of a fully machined and honed cylinder from which the land 16 is omitted.

Another feature of the accumulator disclosed in Figs. 1 and 2 is the arrangement of the cylinder heads 11 and 12 in the ends of the cylinder 10. The cylinder head 11 consists of a disk-like metal member having a centrally located coupling 23 to be connected to the hydraulic system.

The cylinder head 12 is also a disk-like member having an air check valve 24 therein through which air may be introduced to oppose the movement of the piston.

The cylinder heads 11 and'12 are essentially the same except for the coupling 23 and the air check" valve 24, so only one of them will be described.

. As b s shown in H s r ie cylinder head 12 is-r cei ved in an enlargement 25in the ri end, of the cylinder, the inner end of theenlarg ment lei. terminating at a. hauna 26 spaced inwardly from the end of the cylinder. The cylinder head ll, therefore, can slide into the cylinder to an innermost position against, the shoulder 26. The cylinder head also has a peripheral groove 27 in it for receiving a compressible seal 28 to prevent leallcage past the'cylinder hea d. The cylinder head 12. is, retained in the. end of the. cylinder by means of a split ring 29 which, as shown Fig. '2 has a narrow body portion 30 extending throughout the major portion of its length. It has at its opposed ends inwardly extending enlargements 31 and Z22 which are provided with holes or apertures 33 and 34 to. receive a tool to compress. the ends and thereby free the. ring from the, annular groove 35, which is formed in the inner wall of the cylinder adjacent the outer end of the cylinder.

' The cylinder head 12 has a'projecting end portion 36 which fits within the. ring 30 and e ngag es or substantially engages the inner periphery of the split ring 29. Thus, when'the cylinder head 12 is in the position shown in Fig. 1, and abutting against the ring 29, the ends 31 and 320i the ring cannot be compressed inwardly to release the ring and, accordingly, the cylinder head cannot be removed. Inasmuch as the cylinder head is forced outwardly when pressure is present in the cylinder, it will be evident that the cylinder head cannoi be removed until pressure of the gas and the liquid therein is reduced to a safe value. When the gas and liquid pressure are reduced to a safe value, the cylinder head 12 can be forced inwardly into contact with the shoulder and the snap ring 29 then is free from the extension 3t? and can be compressed and removed The above-described connection for retaining the cylinder head in the cylinder is a very desirable safety featiire and prevents accidents while servicing the accumulaton i The above-described accumulator is entirely satisfactory for use in high pressure hydraulic systems but it does not operate as satisfactorily in low pressure systems because the pressure differential between atmosphere and the gas and liquid pressures in the accumulator is insnfiicient to prevent leakage past the compressible seals.

3 of the drawing illustrates a modified type of accumulator which is highly effective for preventing leakage in the accumulator even in low pressure hydraulic systems. The accumulator illustrated in Fig. 3, is similar to that described above in that it includes a cylinder 40, a piston 41 reciprocable therein and cylinder heads 42 and 43, like those shown in Figs. 1 and 2. The principal dilference resides in the provision of a radial opening 44 through the wall of the accumulator which is connected to a small bag-type accumulator 45 of conventional type.

The accumulator 45 supplies gas or fluid under pressure,

as may he desired, at a higher pressure than the pressure of the air or the liquid in the accumulator cylinder 40, to maintain a high pressure difierential on opposite sides of the compressible seals 46 and 47. The high pressure dilferential between the seals maintains them in tight sealing engagement with the cylinder and the piston so that leakage past the seals 46 and 47 is minimized.

Fig. 4 illustrates still another type of accnmulator which also has the advantage of providing reduced areas of sliding contact between the surfaces of the piston and the cylinder. The accumulator shown in Fig. 4 includes a cylinder 50 having a cylinder head 51, like those described above, at one end and a fixed cylinder head 52 at the other end. The accumulator has a substantially cylin: drical inner surface 53 within which a poston 54 slides. The height of the piston 54 is relatively small so that it ese a r l e y sm oute ut we r q i n ca finis gs- Th pistes has a a des we new far s ess-a which extends through a central opening 56 in the cylinder head 52 and is iniise'alin'g relation thereto bcaus e of" s passage 60 in the piston communicating at its ends with a peripheral groove 61'bet ween the compressible seals 58 and '59 and at'its cente'rwith an axialpassage 62 extending F lengthwise of the piston rhd 55. The atmospheric pres sure maintained in the groove 61 is far below the pressures on the qr es ts s de t s P te- 9 t a effective s is maintained between the piston 54 andithe cylinder 50 in an accumulator for ihigh pressure hydraulic system.

The sealing ring arrangement disclosed in Fig. 4 may also be used in other hydraulic devices, such as hydraulic iacl rs and. the like. Inasmuch as the rings are forced against one side er the, receiving. groovefat all times, back-lash or hesitation in the movement of the piston caused by shifting of the sealing 'rings in their growers completely eliminated. i

If an accumnlator like that disclosed in Fig. 4 is to be used a low-pressure hydraulic system, the piston rod may be, provided, with a bag or diaphragm accumulator connected to the here or passage 62 tdmaintain a higher. pressure in the groove 61 than the pressure in the gas and liquid-receivingchambers on opposite sides oi the" piston,' thereby maintaining the conditions. necessary for efiective sealing action of the compressible e fies From the preceding description, it will be apparent that I have provided accumulators which are easier to manufacture and can be. manufactured at ma ten than prior piston type accumnlators andwhich are safer during servicing and can be. used either in high pressure hydraulic systems or low pressure hydraulic systems, as may be. required. i i

It will be understood that the. accumulator may be modified in size and shape and in the materials used therein and, therefore, the form s' of accumulators described herein should be considered asillustrative.

1. An accumulator comprising a hollow cylinder having an inner wall and cylinder heads at opposite ends thereof, a hollow piston having an open end and a closed end movable lengthwise of said cylinder and having a head at said closed end dividing said cylinder into chant bars on opposite sides of said piston to receive fluid under pressure," said piston having a skirt of a length exceeding half the length of said cylinder between said cylinder heads, a pair of grooves in closely spaced relaiq ax a y o s d cylinde at about t mi -porti n compressible sealing rings mounted in said grooves and engaging said skirt slidably, said sealing rings defining an annular fluid-receiving space therebetween, and means to maintain in said space a fluid pressure different than the pressure of the fluid in said chambers.

Z. An accumulator comprising a hollow cylinder hav ing an innfer wall and cylinder heads at opposite ends thereof, a hollow piston having an open end and a closed end movable lengthwise of said cylinder and having a. head at said closed end dividing said cylinder into chamhers on opposite sides of said piston to receive fluid under pressure, said piston having a slgirt of a length exceeding half the length of said cylinder between said cylinder heads, a narrow annular bearing surface extending inwardly from the inner wall of said cylinder at the midportion of said cylinder and receiving the skirt of said pistonslidahly and al ppcrting the major portion of the e th 9? h irt i ass e a io o sai n e wa of aid quads! .wmp s ea ing rings. m un ed in sa bearing surface in spaced relation axially of said cylinder 5 sha in said k rt s dab y, said ea g r ngs efin n w ring snags therehstween a d steam to maintain in said space a fluid pressure diflerent than the pressure of the fluid in said chambers.

3. An accumulator comprising a hollow cylinder having an inner wall and cylinder heads at opposite ends thereof, a piston movable lengthwise of said "cylinder and dividing said cylinder into chambers at opposite ends of said cylinder to receive fluid under pressure, said piston having a length exceeding half the length of said cylinder between said heads, a narrow annular bearing surface extending inwardly from the inner wall of said cylinder at the mid-portion of said cylinder and receiving said piston slidably, compressible sealing rings mounted in said bearing surface in spaced relation axially of said cylinder and engaging said piston slidably, said sealing rings defining an annular fluid-receiving space th'erebetween, a passage in the cylinder having one end coinmunicating with said annular fluid receiving space, and a second accumulator connected with said passage to maintain a higher pressure in said space than the pressure in said chambers.

References Cited in the file of this patent UNITED STATES PATENTS 10 2,281,145 Duey Apr. 28, 1942 2,440,065 Ashton Apr. 20, 1948 2,611,505 Winborn et al. Sept. 23, 1952 2,662,663 Schmidt et al. Dec. 15, 1953 

